Spatial frequency filter device for use with a laser beam, spatial frequency filter arrangement comprising such a spatial frequency filter device, and method for spatial frequency filtering of a laser beam

Description

[0001] The invention relates to a spatial frequency filter arrangement for a laser beam and a method for spatial frequency filtering a laser beam.

[0002] German patent application DE 10 2004 058 044 A1 discloses a spatial frequency filter device for spatial frequency filtering of laser beams. The device comprises a transmission body that is at least partially transparent to the laser radiation and an element having an aperture arranged adjacent to the transmission body or integrated into the transmission body. The element has a diffractive and / or refractive deflection structure. By means of such a diffractive aperture, unwanted light components of a laser beam are specifically diffracted into well-defined solid angles, where they can be efficiently absorbed. Such a diffractive aperture or aperture aperture can, for example, limit the beam emerging from a transport fiber for laser radiation at the output of the transport fiber and protect downstream components.The diffractive region of such an aperture prevents interaction of fringe fields with the respective aperture geometry, especially with aperture edge areas that are otherwise suboptimal due to manufacturing, which could influence the propagation behavior of the useful beam. Aperture apertures without a diffractive region can create virtual sources with undesired propagation directions, which can place a strain on downstream optics or a workpiece being processed.

[0003] While this is avoided with a diffractive aperture, as described in DE 10 2004 058 044 A1, it is difficult or even impossible to filter out unwanted beam components that overlap a main beam or a useful beam. This becomes even more difficult the more these unwanted beam components overlap with the actual useful or main beam.

[0004] From DE 10 2011 102 355 A1 a system for determining the topography of the cornea of ​​an eye is known, comprising an element for generating rings similar to Placido discs and an illumination unit, which are arranged in an illumination beam path, as well as an image recording unit arranged in a detection beam path and a control and evaluation unit, wherein the element for generating rings similar to Placido discs is a fresnled axicon with ring-shaped structures of different radii, between the illumination unit and the fresnled axicon an optical element for the full-surface illumination of the fresnled axicon with ring-shaped, plane waves and an optical element for the separation of the illumination and detection beam paths are arranged and wherein the image recording unit consisting of an imaging system and an image sensor for a telecentric,distance-independent image capture.,

[0005] Diffraction gratings for generating circular interference patterns are known from the scientific publication SOLAK HH ET AL: "Patterning of circular structure arrays with interference lithography", JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B: MICROELECTRONICSPROCESSING AND PHENOMENA, AMERICAN VACUUM SOCIETY, NEW YORK, NY, US, Vol. 21, No. 6, 1 November 2003 (2003-11-01), pages 2883-2887, XP002374099, ISSN: 0734-211X, D01: 10.1116 / 1.1622943.

[0006] The invention is based on the object of creating a spatial frequency filter arrangement and a method for spatial frequency filtering of a laser beam, wherein the aforementioned disadvantages do not occur.

[0007] The object is achieved by a spatial frequency filter arrangement according to claim 1.

[0008] The spatial frequency filter device of the spatial frequency filter arrangement has a neutral region configured to transmit or reflect the laser beam. The spatial frequency filter device has a deflection region radially adjacent to the neutral region, which is configured to deflect beam components of the laser beam from a beam axis of the laser beam. The deflection region has a constant section in which a deflection effect on the beam components of the laser beam for each location in the constant section is independent of the distance of the location from the neutral region. The deflection region also has a variation section in which the deflection effect on the beam components of the laser beam varies depending on the distance from the neutral region. The constant section of the deflection region makes it possible to reliably and effectively deflect and thus filter unwanted beam components that are sufficiently separated from the main or useful beam.The variation section of the deflection range, in contrast, allows for a particularly gradual filtering of unwanted beam components that are located very close to or overlap with the main or useful beam, without adversely affecting or excessively clipping the main or useful beam. Thus, the spatial frequency filter device proposed here provides an improved possibility for filtering a laser beam and, in particular, for removing unwanted beam components that are superimposed on the main or useful beam.

[0009] The neutral range is, in particular, a region of the spatial frequency filter device in which the laser beam is transmitted or reflected without interference, i.e., in particular, without deflection of beam components from the beam axis. The neutral range is therefore particularly configured to transmit or reflect the laser beam without interference.

[0010] A radial direction is understood here to be a direction perpendicular to the beam axis. The beam axis is, in particular, a propagation axis of the laser beam. Accordingly, it refers, in particular, to a propagation direction of the laser beam or extends in the propagation direction of the laser beam. In particular, the beam axis is an axis that coincides with the Poynting vector of the laser beam.

[0011] The fact that the effect varies in the variation section means, in particular, that a deflection efficiency, in particular a strength of a phase modulation, varies depending on the location in the variation section. In contrast, a deflection direction or a deflection angle is / are preferably constant even in the variation section.

[0012] The fact that the deflection effect on the beam components of the laser beam is independent of the distance of the location from the neutral region for each location in the constant section means that a constant deflection effect is present in the constant section that is not location-dependent. Accordingly, in the constant section, both the deflection angle or direction, as well as the strength or intensity of the deflection, are location-independent and thus constant.

[0013] The fact that the deflection effect in the variation section varies depending on the distance from the neutral region means, in particular, that locations in the variation section that are at the same distance from the neutral region have the same deflection effect, in particular, the same deflection intensity. In contrast, locations that are at different distances from the neutral region preferably have a different deflection effect, in particular, a different deflection intensity.

[0014] The distance of a location in the variation section to the neutral region is preferably measured perpendicular to an imaginary or real boundary line between the variation section and the neutral region. The distance is measured in particular depending on the shape or geometry of the imaginary or real boundary line or of the neutral region. If, for example, the neutral region is circular, the distance is preferably measured radially to the circular neutral region. If, however, the neutral region is rectangular, for example, the distance is preferably measured perpendicular to a boundary edge of the neutral region.

[0015] The neutral region can be circular, elliptical, oval, rectangular, or any other geometry. It is preferably adapted to the cross-sectional geometry of a laser beam to be filtered. The shape of the deflection region preferably corresponds to the shape of the neutral region. This applies in particular to both the constant section and the variation section.

[0016] According to a preferred embodiment, the variation section is arranged between the neutral range, on the one hand, and the constant range, on the other. This advantageously results in a transition in the deflection effect from the neutral range to the constant range, in particular a transition from 0% deflection effect in the neutral range to 100% deflection effect in the constant range, preferably a continuous or steady, in particular a linear or Gaussian transition—in particular in the form of a half-Gaussian function. In this way, in particular, unwanted beam components superimposed on the main or useful beam can be filtered out without excessively impairing or clipping the main or useful beam.

[0017] According to a preferred embodiment, the deflection region is followed by a blanking region in which the laser beam is absorbed. In this way, beam components outside the beam to be filtered can be blanked out.

[0018] According to a further development of the invention, the neutral region is arranged centrally and encompassed by the deflection region on the outside, in particular radially outward. The variation section is arranged radially between the neutral region and the constant section. The neutral region is accordingly in particular a central neutral region, which is adjoined radially on the outside by the deflection region, which preferably has the constant section as the outer constant section and the variation section as the inner variation section. Viewed in the radial direction, therefore, from radially inside to radially outside, first the neutral region follows, then the variation section, and finally the constant section. This represents a particularly simple embodiment of the spatial frequency filter device.

[0019] Alternatively, it is possible for the neutral region to be arranged radially outward, with the deflection region adjoining it radially inward, with the variation section also being arranged between the neutral region and the constant section. In this case, the constant section, in particular, is a central constant section, adjoined radially outward by the variation section, which in turn is adjoined radially further out by the neutral region. Such a design, which is essentially the inverse of the previously described design, also represents a very suitable option for filtering a laser beam.

[0020] According to a further development of the invention, the deflection effect on the beam components of the laser beam in the variation section increases with increasing distance from the neutral region. As already indicated, this is particularly advantageous because it allows undesired beam components superimposed on the main or useful beam to be filtered in a particularly suitable manner without excessively impairing the main or useful beam itself, wherein, in particular, undesired effects such as diffraction at edges are avoided or at least reduced. As also already explained, the deflection effect increases from the neutral region to the constant section in the variation section, preferably from 0% at the boundary or in the transition region to the neutral region, up to 100% at the boundary or in the transition region to the constant section.The value of 0% corresponds to the deflection effect present in the neutral range, preferably no deflection effect at all, while the value of 100% corresponds to the deflection effect present in the constant section. Particularly preferably, the deflection effect in the variation section increases continuously or steadily, most preferably linearly, with increasing distance from the neutral range.

[0021] According to a development of the invention, the deflection region has a phase-influencing structure. Preferably, the amplitude of the laser radiation is not influenced in the deflection region. In a preferred embodiment, the deflection region thus acts exclusively on the phase of the laser radiation. The phase-influencing structure is preferably constant in the constant section, while in the variation section it varies with respect to at least one property depending on location, in particular depending on the distance from the neutral region. Suitable phase-influencing structures are known, for example, from Farn, MW Binary gratings with increased efficiency. Appl. Opt. 31(22), 4453-4458 (1992); Ngcobo, S. et al. A digital laser for on-demand laser modes. Nat. Commun. 4:2289 doi: 10.1038 / ncomms3289 (2013); Eckstein W. et al. Comparison of different simulation methods for effective medium computer-generated holograms. Opt. Express 21(10), 12424-12433 (2013).

[0022] According to a further development of the invention, the phase-influencing structure is designed as a diffractive deflection structure. The diffractive deflection structure is periodic with a specific, preferably constant, modulation period and has a constant modulation amplitude in the constant range, wherein the modulation period and the modulation amplitude determine the phase influence of the laser radiation by the diffractive deflection structure. In particular, the modulation amplitude determines the strength of the phase influence, which is also referred to as phase modulation. In the variation section, the modulation amplitude of the diffractive deflection structure varies.

[0023] According to a preferred embodiment, the diffractive deflection structure is designed as a geometric grating. In this case, the modulation amplitude of the diffractive deflection structure is understood to be a geometric height or depth of the diffractive deflection structure—preferably measured along the beam axis. The modulation amplitude is then a grating height of the geometric grating.

[0024] According to another preferred embodiment, the diffractive deflection structure is formed by a local, in particular spatial, variation of a refractive index. Particularly preferably, the diffractive deflection structure is designed as a volume grating.

[0025] The modulation period is, in particular, the period length of the diffractive deflection structure measured perpendicular to the beam axis, i.e., in the radial direction. The modulation period is preferably constant in both the constant section and the variation section, in particular, the same in both the constant section and the variation section.

[0026] According to a further development of the invention, the deflection effect on the beam components of the laser beam in the variation section varies according to a specific function of the distance from the neutral region. In this way, the deflection effect and thus the overall behavior of the spatial frequency filter device can be advantageously influenced in a well-defined manner. As already explained, a preferred embodiment of such a variation of the deflection effect represents a linear function. However, according to another embodiment, it is also possible for the specific function to be a Gaussian function. Other specific functions are also possible.

[0027] According to a further development of the invention, the spatial frequency filter device has a filter body on which the neutral region is formed. The deflection region is applied to the filter body or introduced into the filter body. This represents a particularly simple and at the same time very effective embodiment of the spatial frequency filter device. The filter body is in particular a substrate, preferably made of a material that is transmissive or reflective for the laser radiation. In particular, the diffractive deflection structure is preferably applied to the filter body or introduced into the filter body. In particular, the deflection region / diffractive deflection structure is preferably produced by local modification, in particular structuring, of the filter body, in particular of the material of the filter body.

[0028] According to a further development of the invention, the neutral area has a neutral width dimension. The neutral width dimension is, in particular, a half-width dimension, i.e., a dimension that indicates half a width, or a ring width, in particular a radius.

[0029] The neutral width dimension is preferably from at least 5% to at most 130% of a beam width dimension of a laser beam to be filtered.

[0030] The beam width of the laser beam to be filtered is preferably also a half-width dimension, in particular a radius. In the case of a Gaussian laser beam, the beam width is preferably measured from the beam axis to a point where the laser radiation has dropped to a fraction of 1 / e 2 < of the maximum intensity on the beam axis.

[0031] According to a preferred embodiment, the neutral width preferably ranges from at least 20% to at most 60% of the beam width. This range has proven particularly advantageous for filtering unwanted beam components that overlap with the main or useful beam.

[0032] According to another preferred embodiment, the neutral width preferably ranges from at least 60% to at most 100% of the beam width. This range has proven particularly advantageous for filtering out unwanted beam components that do not overlap, or only overlap to a small extent, with the main or useful beam.

[0033] Alternatively or additionally, the variation section preferably has a variation width dimension. The variation width dimension is also particularly a half-width dimension or a ring width, in particular a radius. The variation width dimension is preferably from at least 10% to at most 150% of the neutral width dimension.

[0034] According to a preferred embodiment, the variation width range is at least 10% to at most 40%, preferably 30%, of the neutral width. This has proven particularly advantageous for filtering unwanted beam components that overlap only slightly or not at all with the main or useful beam.

[0035] According to another preferred embodiment, the variation width range is from at least 40% to at most 150%, preferably 100%, of the neutral width. This embodiment has proven particularly advantageous for filtering unwanted beam components that overlap with the main or useful beam.

[0036] If an area is ring-shaped, the corresponding width measurement is preferably a ring width, i.e. a full width of the ring, measured in a defined direction perpendicular to the boundary lines of the ring, thus quasi a radius section of the outer ring radius attributable to the ring surface.

[0037] According to a further development of the invention, the spatial frequency filter device is designed as a transmission aperture, a lens, a protective glass, a fiber end cap, or a mirror. These represent particularly suitable embodiments of the spatial frequency filter device.

[0038] According to a further development of the invention, the diffractive deflection structure is designed such that it does not generate zero-order diffraction. Thus, unwanted beam sections are deflected as completely as possible from the beam axis.

[0039] Preferably, the diffractive deflection structure is designed to generate only a first order of diffraction, i.e., only first-order diffraction. Thus, unwanted beam components are deflected into a well-defined solid angle, where they can be filtered out easily and precisely.

[0040] According to a preferred embodiment, the diffractive deflection structure comprises a blaze grating or is designed as a blaze grating. This represents a simple yet functional design of the diffractive deflection structure.

[0041] According to a further development of the invention, the diffractive deflection structure is etched into the filter body. This allows the diffractive deflection structure to be produced very easily and with high precision.

[0042] Alternatively, the diffractive deflection structure is preferably incorporated into the filter body as a volume modification, in particular as a volume grating. In this way, modifications can be created with high precision within the volume of the filter body, in particular the substrate, ultimately resulting in regions with different refractive indices.

[0043] The spatial frequency filter arrangement comprises a constant filter device. With the aid of the constant filter device, the unwanted beam components deflected by the spatial frequency filter device can be filtered out, particularly preferably masked out, or in particular absorbed. The spatial frequency filter arrangement provides the advantages explained in connection with the spatial frequency filter device.

[0044] A constant filter device is understood to be a device which has, on the one hand, only a neutral region and, on the other hand, a blanking region adjoining the neutral region. In this case, it is possible for the neutral region to be designed as a central neutral region which is encompassed radially outwards by the blanking region. However, an inverse arrangement is also possible, in which the neutral region encompasses the central blanking region radially outwards. The neutral region transmits or reflects the laser radiation with as little interference as possible, preferably completely interference, while the blanking region preferably neither transmits nor reflects the laser radiation, preferably absorbs it. The constant filter device therefore has, in particular, no deflection region, in particular neither a constant section nor a variation section.

[0045] The constant filter device is preferably designed as a diaphragm, in particular as an aperture diaphragm.

[0046] According to a preferred embodiment, the constant filter device is arranged behind the spatial frequency filter device as seen in the beam propagation direction of the laser beam.

[0047] In particular, the constant filter device is preferably arranged at a distance of a specific propagation distance from the spatial frequency filter device. Beam components deflected by the deflection range of the spatial frequency filter device are then advantageously filtered out by the constant filter device, since they propagate with a higher divergence angle than the desired main or useful beam, so that after the specific propagation distance they are sufficiently spatially separated from the main or useful beam and can thus be eliminated, in particular absorbed, by the constant filter device.

[0048] The spatial frequency filter arrangement is thus particularly designed for amplitude filtering of the laser beam.

[0049] The spatial frequency filter arrangement has a first converging lens, which is arranged downstream of the spatial frequency filter device in the beam propagation direction of the laser beam. The first converging lens can advantageously influence the laser radiation filtered by the spatial frequency filter device. The first converging lens is preferably arranged upstream of the constant filter device in the beam propagation direction of the laser beam. In this way, the laser radiation can be imaged, in particular, onto the constant filter device by means of the first converging lens in order to achieve particularly effective filtering.

[0050] Alternatively, it is possible for the constant filter device to be integrated into the first converging lens, or for the first converging lens to be designed as a constant filter device. In particular, the first converging lens can be opaque in a radially outer region or have its lens effect limited; or the lens effect is eliminated in the radially outer region; or the first converging lens is arranged in a housing, wherein the housing forms the blocking region. The first converging lens can also be encompassed by a cooled absorber or arranged on a cooled absorber that provides the blocking region.

[0051] According to a further development of the invention, the spatial frequency filter arrangement—alternatively or in addition to the first converging lens—comprises a second converging lens arranged upstream of the spatial frequency filter device in the beam propagation direction of the laser beam. This second converging lens can advantageously expand the laser beam upstream of the spatial frequency filter device. This proves particularly advantageous when the laser beam has a very small beam diameter, so that—without the second converging lens—very small structure sizes would be required for the spatial frequency filter device. If the laser beam is expanded in this case, the spatial frequency filter device can have correspondingly larger structures, so that it can be manufactured more simply and cost-effectively.It is therefore particularly advantageous to provide the second converging lens when the laser radiation exits or is coupled out of a fiber bundle upstream of the spatial frequency filter device and therefore has a particularly small beam diameter. In general, the beam width can be adapted to an outer diameter of the spatial frequency filter device, in particular, reduced or enlarged, using the second converging lens. This also proves advantageous when the beam diameter is larger than the outer diameter of the spatial frequency filter device.

[0052] Alternatively or additionally, the spatial frequency filter arrangement preferably comprises a third converging lens, which is arranged downstream of the constant filter device in the beam propagation direction of the laser beam. This can be used—separately or in combination with the first converging lens and / or the second converging lens—to influence, in particular shape, the laser beam at the output of the spatial frequency filter arrangement for subsequent elements or a workpiece to be processed. In particular, the laser beam can be collimated by the third converging lens.

[0053] According to a particularly preferred embodiment, the spatial frequency filter arrangement has a so-called 4f arrangement, where 4f stands for four focal lengths. In such a configuration, the following elements are arranged one after the other in the specified order in the beam propagation direction: the spatial frequency filter device, the first converging lens, the constant filter device, and the third converging lens. Preferably, the constant filter device, on the one hand, and the spatial frequency filter device, on the other hand, are each arranged at the focus of the first converging lens, with the constant filter device preferably also being arranged at the focus of the third converging lens. With such an arrangement, the laser radiation can be particularly well filtered and preferably simultaneously collimated.

[0054] In such a 4f arrangement, it is possible for the second converging lens to be arranged upstream of the spatial frequency filter device in the beam propagation direction. However, it is also possible for the spatial frequency filter arrangement in this preferred embodiment not to have a second converging lens.

[0055] The object is finally also achieved by a method for spatial frequency filtering a laser beam according to claim 11. The neutral range of the spatial frequency filter device is irradiated by the laser beam, or the laser beam is reflected by the neutral range of the spatial frequency filter device. Beam components of the laser beam are deflected from a beam axis of the laser beam in the deflection range radially adjacent to the neutral range. The beam components are deflected in the constant section of the deflection range with a constant deflection effect, regardless of a distance from the neutral range. The beam components are deflected in the variation section of the deflection range arranged between the neutral range and the constant section, depending on a distance from the neutral range, with a varying deflection effect.Particularly preferably, the beam components in the variation section are deflected as a function of the distance to the neutral region, with the deflection effect increasing with increasing distance from the neutral region.

[0056] In connection with the method, the advantages arise in particular which have already been explained in connection with the spatial frequency filter device and the spatial frequency filter arrangement.

[0057] In a preferred embodiment, a spatial frequency filter device according to the invention or a spatial frequency filter device according to one of the previously described embodiments is used within the scope of the method. Alternatively or additionally, a spatial frequency filter arrangement according to the invention or a spatial frequency filter arrangement according to one of the previously described embodiments is preferably used within the scope of the method. This results in the advantages already described in a particular manner.

[0058] According to a further development of the invention, the deflection region comprises a diffractive deflection structure. Preferably, the diffractive deflection structure suppresses a zeroth order of diffraction. Particularly preferably, the diffractive deflection structure generates exclusively a first order of diffraction.

[0059] According to a further development of the invention, it is provided that the beam components deflected in the deflection region are deflected away from the beam axis of the laser beam by a deflection angle which results as the arcsine of the quotient of a wavelength of the laser radiation divided by a modulation period of the deflection region, in particular a modulation period of the diffractive deflection structure, in particular according to the following formula: θ = sin − 1 λ g .

[0060] Where θ is the deflection angle, λ is the wavelength of the laser radiation, and g is the modulation period of the deflection range. The deflection angle is preferably approximately calculated as the quotient of the wavelength of the laser radiation and the modulation period, in particular according to the following formula: θ ≈ λ g .

[0061] For example, if the modulation period is 10 µm, the deflection angle for infrared radiation is approximately 5.7°. For green light, it is approximately half that.

[0062] Preferably, beam components deflected by the deflection region of the spatial frequency filter device are eliminated, in particular absorbed, by a constant filter device preferably arranged at a distance from the spatial frequency filter device by a certain propagation distance.

[0063] In this way, in particular, an amplitude filtering of the laser beam is carried out.

[0064] The invention is explained in more detail below with reference to the drawings, which show: Figure 1 shows a schematic representation of a spatial frequency filter device according to the prior art; Figure 2 shows a schematic representation of an exemplary embodiment of a spatial frequency filter device according to the invention; Figure 3 shows a schematic representation of a first exemplary embodiment of a spatial frequency filter arrangement; and Figure 4 shows a schematic representation of a second exemplary embodiment of a spatial frequency filter arrangement.

[0065] Fig. 1shows a schematic representation of a spatial frequency filter device 100 according to the prior art. The spatial frequency filter device 100 is configured for use with a laser beam 200, which is coupled out of a fiber or fiber bundle 10, for example. The laser beam 200 is a divergent laser beam. However, it is equally possible to use such a spatial frequency filter device 100 with a collimated laser beam 200.

[0066] The spatial frequency filter device 100 has a neutral region 110 configured to transmit the laser beam 200. However, the neutral region 110 can also be configured to reflect the laser beam 200.

[0067] Adjacent to the neutral region 110 is a deflection region 120 configured to deflect beam components 210 of the laser beam 200 from a beam axis A of the laser beam 200. A total deflection angle β results from, on the one hand, a deflection angle θ determined by the deflection region 120 and, on the other hand, an aperture angle α of the divergent laser beam 200. If the laser beam 200 is configured as a collimated laser beam, it is deflected by the deflection region 120 only by the deflection angle θ. Beam components 210 deflected by the deflection region 120 are then filtered out by a constant filter device 320.This is possible because they propagate with an increased divergence angle compared to the desired main or useful beam, so that after a certain propagation distance they are sufficiently spatially separated from the main or useful beam and can thus be eliminated by the constant filter device 320, in particular by a conventional absorption element.

[0068] The deflection effect of the deflection region 120 in the spatial frequency filter device 100 known from the prior art is location-independent, i.e., constant everywhere in the deflection region 120.

[0069] Fig. 2shows a schematic representation of an embodiment of a spatial frequency filter device 100. Identical and functionally identical elements are provided with the same reference numerals in all figures, so that reference is made to the preceding description in each case. The spatial frequency filter device 100 differs from the known spatial frequency filter device 100 according to Figure 1in particular in that the deflection region 120, in addition to a constant section 123 in which a deflection effect on the beam components 210 of the laser beam 200 for each location in the constant section 123 is independent of a distance of the location from the neutral region 110, has a variation section 125 in which the deflection effect on the beam components 210 of the laser beam 200 varies depending on a distance from the neutral region 110. In this way, it is particularly possible to filter out beam components 210 that are arranged close to the main or useful beam or that overlap with the main or useful beam, without the main or useful beam being unduly impaired or adversely affected. The variation in the deflection effect relates in particular to a deflection efficiency, in particular to a strength of a phase modulation.In contrast, the deflection angle is preferably constant regardless of location and is in particular the same in the constant section 123 and the variation section 125.

[0070] The variation section 125 is arranged in particular between the neutral region 110 and the constant section 123.

[0071] In the embodiment shown here, the neutral region 110 is arranged centrally, with the deflection region 120 radially adjoining the neutral region 110. The deflection region 120 has the constant section 123 as the outer constant section and the variation section 125 as the inner variation section, with the variation section 125 adjoining the neutral region 110 radially on the inside, and the constant section 123 adjoining the variation section 125 radially on the outside.Preferably, the various regions / sections are circular, wherein the variation section 125 preferably surrounds the central neutral region 110 in a ring-shaped manner, and wherein the constant section 123 in turn surrounds the variation section 125 radially on the outside in a ring-shaped manner, so that the variation section 125 is arranged as an annular region between the neutral region 110, which is in particular designed in the shape of a circular disk, and the annular constant section 123 designed as an outer ring.

[0072] However, an inverse design is also possible, in which the constant section 123 of the deflection region 120 is arranged centrally, to which the variation section 125 then immediately adjoins radially outwards, which in turn is adjoined radially outwards by the then outer neutral region 110.

[0073] The deflection effect on the beam components 210 of the laser beam 200 preferably increases in the variation section 125 with increasing distance from the neutral region 110.

[0074] Preferably, the deflection effect on the beam components 210 in the variation section 125 varies according to a specific function of the distance from the neutral region 110, particularly preferably according to a Gaussian function or according to a linear function.

[0075] The deflection region 123 preferably has a phase-influencing structure 126, which is constant in the constant section 123 and varies in the variation section 125. Particularly preferably, the spatial frequency filter device 110 influences exclusively the phase, but not the intensity or amplitude, of the laser beam 200. This has the advantage that the laser beam 200 ultimately has the same intensity distribution—except for the filtered, unwanted beam components 210—in the beam propagation direction downstream of the spatial frequency filter device 100 as upstream of the spatial frequency filter device 100.

[0076] The phase-influencing structure 126 is preferably designed as a diffractive deflection structure 127, wherein the diffractive deflection structure 127 has a modulation period g, thus being periodic, and has a constant modulation amplitude a in the constant section 123. In the variation section 125, however, the modulation amplitude a of the diffractive deflection structure 127 varies. Preferably, the modulation amplitude a in the variation section 125 varies according to a specific function of the distance from the neutral region 110, in particular according to a Gaussian function or according to a linear function.

[0077] The diffractive deflection structure 127 can be designed in particular as a geometric grating, or formed by a local, in particular spatial, variation of a refractive index.

[0078] The spatial frequency filter device 100 preferably has a filter body 130 on which the neutral region 110 is formed. The deflection region 120 is preferably applied to the filter body 130 or incorporated into the filter body 130.

[0079] In Figure 2 A neutral width dimension NB is also shown, which is the neutral area 110. The neutral width dimension NB here is preferably a radius of the neutral area 110.

[0080] The spatial frequency filter device 100 is preferably designed as a transmission aperture, a lens, a protective glass, a fiber end cap, or a mirror. In particular, the spatial frequency filter device 100 can also be integrated into a resonator of a laser generating the laser beam 200, arranged downstream of the resonator, or arranged upstream of or within a processing optics. However, it is also possible for the spatial frequency filter device 100 to be designed as a separate element.

[0081] The diffractive deflection structure 127 is preferably designed such that it does not generate zero-order diffraction. Preferably, the diffractive deflection structure 127 is designed such that it generates only first-order diffraction, in particular, no higher orders of diffraction. According to a preferred embodiment, the diffractive deflection structure 127 is designed as a blaze grating 129 or it has a blaze grating 129.

[0082] According to a preferred embodiment, the diffractive deflection structure 127 is etched into the filter body 130 or introduced into the filter body 130 as a volume modification, in particular as a volume grating.

[0083] Fig. 3shows a schematic representation of a first exemplary embodiment of a spatial frequency filter arrangement 300 for the laser beam 200, wherein the spatial frequency filter arrangement 300 comprises a spatial frequency filter device 100 in accordance with the technical teaching disclosed here. It is shown here on the spatial frequency filter device 100 that the variation section 125 has a variation width dimension VB, which is preferably a ring width of the annular variation section 125, with which the annular variation section 125 surrounds the neutral region 110 in a ring-like manner.

[0084] Furthermore, schematically in Figure 3 a beam width dimension SB of the laser beam 200 is shown, which is also designed as a half-width dimension, here as a beam radius, where specifically in Figure 3twice the beam width dimension is represented as the diameter of the laser beam 200. The beam width dimension is preferably determined at a fraction of 1 / e 2< of a maximum intensity for the laser beam 200, which is represented here as Gaussian by way of example.

[0085] The neutral width dimension NB is preferably from at least 5% to at most 130% of the beam width dimension SB. Alternatively or additionally, the variation width dimension VB of the variation section 125 is preferably from at least 10% to at most 150% of the neutral width dimension NB.

[0086] Figure 3schematically shows a situation in which the unwanted beam components 210 are at a comparatively large distance from the beam axis A and, at the same time, from the main or useful beam, so that they can be filtered out comparatively easily. In such a case, the neutral width dimension NB is preferably from at least 60% to at most 100% of the beam width dimension SB. The variation width dimension VB is preferably from at least 10% to at most 40%, preferably 30%, of the neutral width dimension NB.

[0087] Already here is Figure 4 where - regardless of the otherwise different design of the second embodiment of the spatial frequency filter arrangement 300 shown there - a situation is shown in which the unwanted beam components 210 overlap with the main or useful beam and are thus arranged closer to the beam axis A than according to the situation shown in Figure 3is shown. In this case, the unwanted beam components are more difficult to filter. The neutral width dimension NB is preferably selected to be at least 20% to at most 60% of the beam width dimension SB. The variation width dimension VB in this case is preferably at least 40% to at most 150%, preferably 100%, of the neutral width dimension NB.

[0088] Returning to Figure 3The spatial frequency filter arrangement 300 shown therein has the constant filter device 320 downstream of the spatial frequency filter device 100 in the beam propagation direction of the laser beam 200—in particular, spaced therefrom by a specific propagation distance. It also has a first converging lens 310, which is arranged downstream of the spatial frequency filter device 100. Furthermore, the first converging lens 310 is arranged upstream of the constant filter device 320. Alternatively, it is also possible for the constant filter device 320 to be integrated into the first converging lens 310 or to be arranged on the first converging lens 310. Unwanted beam components deflected by the deflection region 120 are eliminated, in particular absorbed, by the constant filter device 320 after passing through the specific propagation distance. In this way, in particular, amplitude filtering for the laser beam 200 is realized.

[0089] The spatial frequency filter arrangement 300 according to the first embodiment of Figure 3also has a second converging lens 330, which is arranged upstream of the spatial frequency filter device 100 in the beam propagation direction of the laser beam 200. This proves particularly advantageous when the laser beam 200 has a very small beam width SB, in particular when it is coupled out of a fiber bundle 10, wherein it can then be expanded by the second converging lens 330, so that the spatial frequency filter device 100 can have a larger structural size, in particular a larger modulation period g and / or a larger modulation amplitude a, than would be the case if the laser beam 200 were not expanded. In general, the beam width SB can be adapted to an outer diameter of the spatial frequency filter device 100, in particular reduced or enlarged, by means of the second converging lens 330. This also proves advantageous when the beam width SB is larger than the outer diameter of the spatial frequency filter device 100.

[0090] In the first exemplary embodiment illustrated here, the spatial frequency filter arrangement 300 also has a third collection line 340, which is arranged downstream of the constant filter device 320 in the beam propagation direction of the laser beam 200. This can advantageously be used, in particular, to collimate the filtered laser beam. This results in a filtered, collimated laser beam 220 downstream of the spatial frequency filter arrangement 300. It is schematically illustrated that this filtered, collimated laser beam 220 no longer contains the unwanted beam components 210.

[0091] The laser beam 200 propagates in the Figures 3 and 4 from left to right through the spatial frequency filter arrangements 300.

[0092] Fig. 4shows a schematic representation of a second embodiment of a spatial frequency filter arrangement 300. The second embodiment shown here does not have the second converging lens 330. However, it is also possible in this second embodiment to use such a second converging lens 330.

[0093] Preferably, the spatial frequency filter device 100 is designed according to a so-called 4f arrangement, wherein the spatial frequency filter device 100 and the constant filter device 320 are each arranged in the focus positions on both sides of the first converging lens 310, wherein, moreover, the constant filter device 320 is preferably arranged in the focus of the third converging lens 340.

[0094] In the first embodiment according to Figure 3Additionally, the spatial frequency filter device 100 can be arranged at the focus of the second converging lens 330. However, this is not necessarily the case; rather, an arrangement outside the focus is also possible, in particular in order to adapt the beam width dimension SB to the outer diameter of the spatial frequency filter device 100.

[0095] According to a preferred embodiment, the foci of the various converging lenses 310, 330, 340 are of the same design, but they can also be different in pairs or all of them can be selected differently from one another.

[0096] The laser beam 200 is preferably filtered by the laser beam 200 passing through the neutral region 110 of the spatial frequency filter device 100, or by the laser beam 200 being reflected by the neutral region 110. In this case, the unwanted beam components 210 are deflected from the beam axis A in the deflection region 120 radially adjoining the neutral region 110, wherein the beam components 210 are deflected in the constant section 123 with a constant deflection effect regardless of the distance from the neutral region 110, wherein the beam components 210 are deflected in the variation section 125 with a varying deflection effect depending on the distance from the neutral region 110, in particular with an increasing deflection effect as the distance from the neutral region 110 increases.

[0097] The deflection angle θ of the deflection region 120 is preferably obtained as the arcsine of the quotient of the incident wavelength λ of the laser beam 200, on the one hand, and the modulation period g of the deflection region 120, on the other hand, in particular according to the above-mentioned equation (1). The deflection angle θ is preferably approximately obtained as the quotient of the incident wavelength λ divided by the modulation period g, in particular according to the above-mentioned equation (2).

[0098] The neutral region 110 is preferably geometrically shaped in a plane to which the beam axis A is perpendicular, in such a way that it corresponds at least to the ideal beam geometry of the laser beam 200, in particular circular for a cylindrically symmetrical laser beam 200. However, it can also be rectangular—in particular for a rectangular laser beam cross-section—or elliptical—in particular for an elliptical laser beam cross-section. The deflection region 120, in particular both the constant section 123 and the variation section 125, are preferably shaped like the neutral region 110 and surround it radially on the outside, in particular as correspondingly shaped edge regions.

Claims

1. A spatial frequency filter arrangement (300) for a laser beam (200), with a spatial frequency filter device (100), a first collecting lens (310) which is arranged in the beam propagation direction of the laser beam (200) behind the spatial frequency filter device (100), and a constant filter device (320), wherein the spatial frequency filter device (100) has a neutral region (110) which is configured to transmit or reflect the laser beam (200) and a deflection region (120) radially adjacent to the neutral region (110), which is configured to deflect beam portions (210) of the laser beam (200) from a beam axis (A) of the laser beam (200), wherein the deflection region (120) has a constant section (123) in which a deflection effect on the beam portions (210) of the laser beam (200) is independent of a distance from the neutral region (110) for each location in the constant section (123), wherein the deflection region (120) has a variation section (125) in which the deflection effect on the beam portions (210) of the laser beam (200) varies as a function of a distance from the neutral region (110), wherein the neutral region (110) is arranged centrally and is surrounded on the outside by the deflection region (120), wherein the variation section (125) is arranged between the neutral region (110) and the constant section (123), and wherein the constant filter device (320) is configured to filter out the beam portions (210) of the laser beam (200) deflected by the spatial frequency filter device (100).

2. The spatial frequency filter arrangement (300) according to claim 1, characterized in that the deflection effect on the beam portions (210) of the laser beam (200) in the variation section (125) increases with an increasing distance from the neutral region (110).

3. The spatial frequency filter arrangement (300) according to any one of the preceding claims, characterized in that the deflection region (120) has a phase influencing structure (126).

4. The spatial frequency filter arrangement (300) according to any one of the preceding claims, characterized in that the phase influencing structure (126) is designed as a diffractive deflection structure (127), wherein the diffractive deflection structure (127) is periodic and has a constant modulation amplitude (a) in the constant section (123), wherein the modulation amplitude (a) of the diffractive deflection structure (127) varies in the variation section (125).

5. The spatial frequency filter arrangement (300) according to any one of the preceding claims, characterized in that the deflection effect on the beam portions (210) of the laser beam (200) varies according to a specific function of the distance from the neutral region (110), preferably according to a Gaussian function or according to a linear function.

6. The spatial frequency filter arrangement (300) according to any one of the preceding claims, characterized in that the spatial frequency filter device (100) has a filter body (130) on which the neutral region (110) is designed, wherein the deflection region (120) is applied to the filter body (130) or inserted into the filter body (130).

7. The spatial frequency filter arrangement (300) according to any one of the preceding claims, characterized in that the neutral region (110) has a neutral width size (NB), wherein a) the neutral width size (NB) is at least 5% to at most 130%, preferably from 20% to at most 60%, preferably from at least 60% to at most 100%, of a beam width (SB) of a laser beam (200) to be filtered, and / or b) a variation width size (VB) of the variation section (125) of at least 10% to at most 150%, preferably at least 10% to at most 40%, preferably 30%, preferably from at least 40% to at most 150%, preferably 100%, of the neutral width size (NB).

8. The spatial frequency filter arrangement (300) according to any one of the preceding claims, characterized in that the spatial frequency filter device (100) is designed as a transmission aperture, as a lens, as a protective glass, as a fiber end cap, or as a mirror.

9. The spatial frequency filter arrangement (300) according to any one of the preceding claims, characterized in that the diffractive deflection structure (127) is etched into the filter body (130) or introduced into the filter body (130) as a volume modification.

10. The spatial frequency filter arrangement (300) according to any one of the preceding claims, characterized in that a second collecting lens (330) is arranged in the beam propagation direction of the laser beam (200) in front of the spatial frequency filter device (100).

11. A method for spatial frequency filtering of a laser beam (200), wherein a spatial frequency filter arrangement (300) according to one of claims 1 to 10 is used, wherein a) the neutral region (110) of the spatial frequency filter device (100) is irradiated by the laser beam (200), or b) the laser beam (200) is reflected through the neutral region (110) of the spatial frequency filter device (100); wherein - beam portions (210) of the laser beam (200) in the deflection region (120) radially adjacent to the neutral region (110) are deflected from a beam axis (A) of the laser beam (200), wherein - the beam portions (210) in the constant section (123) of the deflection region (120) are deflected with a constant deflection effect independently of a distance from the neutral region (110), and wherein - the beam portions (210) in the variation section (125) of the deflection region (120) are deflected with a varying deflection effect as a function of a distance from the neutral region (110).

12. The method according to claim 11, characterized in that the deflection region (120) has a diffractive deflection structure (127), wherein a zeroth diffraction order is suppressed by the diffractive deflection structure (127).